Merge pull request #93 from bitfield/fix_truncate_bug_81

Fix #81

.circleci/config.yml

@@ -2,7 +2,7 @@ version: 2
 jobs:
   test:
     docker:
-      - image: circleci/golang:1.12
+      - image: circleci/golang:1.17
     steps:
       - checkout
       - run: go test ./...

README.md

@@ -861,7 +861,7 @@ fmt.Println(err)
 
 ## WriteFile
 
-`WriteFile()` writes the contents of the pipe to a named file. It returns the number of bytes written, or an error:
+`WriteFile()` writes the contents of the pipe to a named file, truncating it if it exists. It returns the number of bytes written, or an error:
 
 ```go
 var wrote int

sinks.go

@@ -105,11 +105,12 @@ func (p *Pipe) String() (string, error) {
 }
 
 // WriteFile writes the contents of the Pipe to the specified file, and closes
-// the pipe after reading. It returns the number of bytes successfully written,
-// or an error. If there is an error reading or writing, the pipe's error status
-// is also set.
+// the pipe after reading. If the file already exists, it is truncated and the
+// new data will replace the old. It returns the number of bytes successfully
+// written, or an error. If there is an error reading or writing, the pipe's
+// error status is also set.
 func (p *Pipe) WriteFile(fileName string) (int64, error) {
-	return p.writeOrAppendFile(fileName, os.O_RDWR|os.O_CREATE)
+	return p.writeOrAppendFile(fileName, os.O_RDWR|os.O_CREATE|os.O_TRUNC)
 }
 
 func (p *Pipe) writeOrAppendFile(fileName string, mode int) (int64, error) {

sinks_test.go

@@ -2,10 +2,11 @@ package script
 
 import (
 	"bytes"
-	"github.com/google/go-cmp/cmp"
 	"io/ioutil"
 	"os"
 	"testing"
+
+	"github.com/google/go-cmp/cmp"
 )
 
 // doSinksOnPipe calls every kind of sink method on the supplied pipe and
@@ -61,12 +62,11 @@ func doSinksOnPipe(t *testing.T, p *Pipe, kind string) {
 func TestAppendFile(t *testing.T) {
 	t.Parallel()
 	orig := "Hello, world"
-	testFile := "testdata/appendfile.txt"
-	defer os.Remove(testFile)
+	path := t.TempDir() + t.Name()
 	// ignore results; we're testing AppendFile, not WriteFile
-	_, _ = Echo(orig).WriteFile(testFile)
+	_, _ = Echo(orig).WriteFile(path)
 	extra := " and goodbye"
-	wrote, err := Echo(extra).AppendFile(testFile)
+	wrote, err := Echo(extra).AppendFile(path)
 	if err != nil {
 		t.Error(err)
 	}
@@ -74,7 +74,7 @@ func TestAppendFile(t *testing.T) {
 		t.Errorf("want %d bytes written, got %d", len(extra), int(wrote))
 	}
 	// check file contains both contents
-	got, err := File(testFile).String()
+	got, err := File(path).String()
 	if err != nil {
 		t.Error(err)
 	}
@@ -297,19 +297,18 @@ func TestString(t *testing.T) {
 	}
 }
 
-func TestWriteFile(t *testing.T) {
+func TestWriteFileNew(t *testing.T) {
 	t.Parallel()
 	want := "Hello, world"
-	testFile := "testdata/writefile.txt"
-	defer os.Remove(testFile)
-	wrote, err := Echo(want).WriteFile(testFile)
+	path := t.TempDir() + t.Name()
+	wrote, err := Echo(want).WriteFile(path)
 	if err != nil {
 		t.Error(err)
 	}
 	if int(wrote) != len(want) {
 		t.Errorf("want %d bytes written, got %d", len(want), int(wrote))
 	}
-	got, err := File(testFile).String()
+	got, err := File(path).String()
 	if err != nil {
 		t.Error(err)
 	}
@@ -317,3 +316,32 @@ func TestWriteFile(t *testing.T) {
 		t.Errorf("want %q, got %q", want, got)
 	}
 }
+
+func TestWriteFileTruncatesExisting(t *testing.T) {
+	t.Parallel()
+	want := "Hello, world"
+	path := t.TempDir() + t.Name()
+	// write some data first so we can check for truncation
+	data := make([]byte, 15)
+	err := os.WriteFile(path, data, 0600)
+	if err != nil {
+		t.Fatal(err)
+	}
+	wrote, err := Echo(want).WriteFile(path)
+	if err != nil {
+		t.Error(err)
+	}
+	if int(wrote) != len(want) {
+		t.Errorf("want %d bytes written, got %d", len(want), int(wrote))
+	}
+	got, err := File(path).String()
+	if err != nil {
+		t.Error(err)
+	}
+	if got == want+"\x00\x00\x00" {
+		t.Fatalf("file not truncated on write")
+	}
+	if got != want {
+		t.Errorf("want %q, got %q", want, got)
+	}
+}